This paper discusses a developmental-descriptive approach to the study of children, adolescent, and adult understanding of interpersonal relationships. A study is reported which compares the level of interpersonal reasoning of children with clinically identified peer relation problems with the reasoning level of a case-control sample of better adjusted peers with similar social class, sex, I.Q. and racial backgrounds. The results of this study are discussed within the context of an attempt to integrate clinical and cognitive-developmental approaches to child and adolescent psychology. (Author)